Research report

Abstract

Data from seafloor observatories are generally of poorer quality then continental site data because the sea surface is an important and local source of broadband noise. This noise is the result of wind and wave action through direct forcing at long periods and by non-linear coupling to elastic waves at short periods. By analysing the noise and looking for patterns we sometimes can constrain the noise source and subtract it from the spectrum and thereby improve the quality of the data. In another case we can use patterns in the spectrum to derive information on the structure of the ocean bottom. This report will present an analysis of broadband noise at two locations in the Pacific. The first location is ODP Site 843B, and is situated about 225km south-west of Oahu at a waterdepth of 4407m. Between February and May 1998, the Ocean Seismic Network Pilot Experiment (OSNPE) acquired over 115 days of broadband borehole seismic data at a sampling rate of 20 samples/second. The other location is situated near 28N latitude, 142W longitude (about halfway between Hawaii and California) at a waterdepth of 5000m. In September 1998, a permanent deep ocean scientific research facility – the Hawaii-2 Observatory, or H2O – was installed on a retired AT&T submarine telephone cable recording broadband seafloor seismic data at 160 samples/second.